Increase in sea level variability with ocean warming associated with the nonlinear thermal expansion of seawater

Sea level variability increasingly contributes to coastal flooding and erosion as global sea levels rise, partly due to the thermal expansion of seawater, which accelerates with increasing temperature. Climate model simulations with increasing greenhouse gas emissions suggest that future sea level variability, such as the annual and interannual oscillations that alter local astronomical tidal cycles and contribute to coastal impacts, will also increase in many regions. Here, we present an analysis of the CMIP5 climate model projections of future sea level to show that there is a tendency for a near-global increase in sea level variability with continued warming that is robust across models, regardless of whether ocean temperature variability increases. Specifically, for an upper-ocean warming by 2 °C, which is likely to be reached by the end of this century, sea level variability increases by 4 to 10% globally on seasonal-to-interannual timescales because of the nonlinear thermal expansion of seawater. As the oceans continue to warm, future ocean temperature oscillations will cause increasingly larger buoyancy-related sea level fluctuations that may alter coastal risks. Sea level variability will increase by up to 10% globally on seasonal-to-interannual timescales for future upper-ocean warming of about 2 °C, because thermal expansion accelerates at higher temperatures, suggest analyses of climate model simulations.